This application is based on the application No. 2001-072172 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an absorption dose measuring apparatus for intensity modulated radio therapy (referred to as xe2x80x9cIMRTxe2x80x9d hereinafter), which is used for measuring or evaluating an integrated three-dimensional absorption dose distribution of an X-ray or a particle beam such as an electron beam in a phantom, in the IMRT process for treating cancers.
2. Description of the Prior Art
IMRT is well known as one of radiation therapy processes. In the IMRT, because a radiation beam is applied to a patient while variously changing the shape of the radiation field of the beam and further variously changing the incident direction of the radiation beam, the integrated absorption dose of the radiation may be set so as to match the shape of the affected part to be treated. Accordingly, the radiation therapy process can be effectively carried out with the radiation accurately focused onto the affected part to be treated.
When the IMRT described above is carried out, a treatment plan is made at first. In the treatment plan, there may be set a condition for accurately applying the radiation onto the affected part to be treated, with a predetermined absorption dose distribution of the radiation. The treatment plan must be then examined or verified through experiments whether it is appropriate to the patient. For the verification, in general, an absorption dose measuring apparatus for IMRT (referred to xe2x80x9cIMRT dosimeterxe2x80x9d hereinafter) is used.
Hereinafter, there will be described a process for measuring an absorption dose distribution in a conventional IMRT dosimeter.
FIG. 6 illustrates a process for measuring an absorption dose distribution in a conventional typical IMRT dosimeter. As shown in FIG. 6, the conventional IMRT dosimeter has a construction that a plurality of X-ray films 103 are interposed at a plurality of positions in a phantom 102 made of a plastic.
In the conventional IMRT dosimeter having the above-mentioned construction, radiation beams 110a and 101b such as X-rays, particle beams such as electron beams or the like are applied to the phantom 102. In consequence, each of the X-ray films 103 interposed in the phantom 102 is exposed (sensitized) due to interactions with the radiation beams. Then, there may be obtained a two-dimensional absorption dose distribution at each of the positions corresponding to the X-ray films 103 by measuring the distribution pattern of darkening degree in the X-ray film 103. Thus, on the basis of the two-dimensional absorption dose distributions of all of the X-ray films 103, a three-dimensional absorption dose distribution in the phantom 102 may be obtained.
In the Japanese Laid-open Patent Publication 9-230053, 10-153662 or 10-153663, there is disclosed a depth dose measuring apparatus which can measure an absorption dose distribution in a phantom in a short duration of time without using X-ray films.
FIG. 7 illustrates a schematic arrangement of a depth dose measuring apparatus, disclosed in the above-mentioned Publication 10-153663, for inspection and verification of a radiation emitter for cancer treatment. As shown in FIG. 7, in the depth dose measuring apparatus, a detecting unit 111 is composed of a plastic-made scintillation fiber block 113 substantially equivalent to the human organism and transparent-plastic blocks 114 sandwiching the fiber block 113. Also, provided is an image sensor 112 for measuring a light intensity distribution on one end of the scintillation fiber block 113.
In the depth dose measuring apparatus, the radiation beam is applied onto the upper surface of the detecting unit 111 in the direction perpendicular to the upper surface from above. Because the detecting unit 111 is substantially equivalent to the human organism, its properties for absorbing the radiation are substantially equal to those of the human organism. Therefore, it can correctly measure the absorption dose distribution. In this case, if the detecting unit 111 and the image measuring device 112 are rotated or linearly moved as one body, a three-dimensional absorption dose distribution in the detecting unit 111 may be measured using a steady radiation beam emitted from a radiation emitter.
However, the conventional IMRT dosimeter using X-ray films, for example shown in FIG. 6, may fail to measure the absorption dose distribution at a desired level of accuracy, because the X-ray film is significantly different in absorbing radiation from the human organism. Also, the X-ray film may vary in output depending on production lot or the conditions of development, even if the absorption dose is uniform. Accordingly, the result of the measurement will hardly be consistent in accuracy. The steps of developing the X-ray film and measuring a pattern of the darkening are time and labor intensive.
On the other hand, in the conventional depth dose measuring apparatus, for example shown in FIG. 7, there exists such a problem that it is applicable to the IMRT with much difficulty, even though it is generally capable of measuring the absorption dose distribution accurately and readily. That is, because the IMRT generally measures or evaluates the integrated absorption dose while variously changing the shape of the radiation field and the incident direction of the radiation beams, the above-mentioned conventional depth dose measuring apparatus, which is to use only a steady radiation beam, may hardly provide appropriate measurement or evaluation of the integrated absorption dose distribution for the IMRT process.
The present invention has been achieved to solve the conventional problems described above, and has an object to provide an IMRT dosimeter which can accurately measure or evaluate a three-dimensional absorption dose distribution in a phantom in a short duration of time for the IMRT process.
According to a first aspect of the present invention, which has been achieved to solve the above-mentioned problems, there is provided an IMRT dosimeter (i.e. absorption dose measuring apparatus for IMRT) which measures (or evaluates) a absorption dose distribution in a phantom for the IMRT, including (i) a detecting section composed of a plastic scintillator and arranged so that its strike is vertical to an incident direction of a radiation beam, (ii) a phantom composed of a transparent plastic and formed (or disposed) to sandwich the detecting section from both sides along a direction parallel with the strike of the plastic scintillator, (iii) an image measuring device for measuring a distribution of intensity of light emitted from one side of the detecting section along the direction parallel with the strike of the plastic scintillator, (iv) an assembly driver for moving an assembly including the detecting section, the phantom and the image measuring device in the direction parallel with the strike of the plastic scintillator, or for rotating the assembly about a rotation axis which extends vertically across a center of the detecting section, and (v) a data processor for processing a data measured by the image measuring device. Hereupon, (vi) the data processor picks (or gathers) a three-dimensional absorption dose distribution data in the phantom when the assembly driver moves the assembly in the direction parallel with the strike of the plastic scintillator or rotates the assembly about the rotation axis, at each of plural radiation beam applications each of which is performed under a predetermined condition. Further, (vii) the data processor obtains an integrated three-dimensional absorption dose distribution in the phantom by summing (or combining, or synthesizing) the three-dimensional absorption dose distribution data for each of the radiation beam applications.
In the IMRT dosimeter of the first aspect of the present invention, the data processor, for example composed of a computer or the like, picks (or gathers) the three-dimensional absorption dose distribution data in the phantom in each of the plural applications of the radiation beams. Further, the data processor obtains the integrated three-dimensional absorption dose distribution for the IMRT by summing the three-dimensional absorption dose distribution for the plural applications of the radiation beams. Because the integrated three-dimensional absorption dose distribution is obtained by the data processing using the computer or the like, the absorption dose distribution may be measured with a higher accuracy in a short period.
In an IMRT dosimeter of a second aspect of the present invention, the IMRT dosimeter of the first aspect is modified so that the detecting section is composed of a plastic scintillator which is formed by bundling plastic scintillation fibers in a block shape.
According to the IMRT dosimeter of the second aspect of the present invention, at first, there may be obtained advantages similar to those of the IMRT dosimeter of the first aspect of the present invention. In addition, because the plastic scintillator formed by bundling the plastic scintillation fibers in the block shape is used, the light produced in the detecting section by the radiation beam can be certainly guided by the scintillation fibers to reach the end surface of the detecting section. In consequence, the distribution of the light intensity in the detecting section can accurately appear at the end surface of the detecting section so that the accuracy of measuring the integrated three-dimensional absorption dose distribution may be improved.
In an IMRT dosimeter of a third aspect of the present invention, the IMRT dosimeter of the first aspect is modified so that the detecting section is composed of a plastic scintillator of a thin plate shape (or form).
According to the IMRT dosimeter of the third aspect of the present invention, at first, there may be obtained advantages similar to those of the IMRT dosimeter of the first aspect of the present invention. In addition, because the detecting section is formed of the plastic scintillator of the thin plate shape, diffusion of the light produced in the detecting section by the radiation beam is reduced so that the accuracy of measuring the integrated three-dimensional absorption dose distribution may be improved. Moreover, the cost for producing the detecting section or the IMRT dosimeter may be reduced.
In an IMRT dosimeter of a fourth aspect of the present invention, the IMRT dosimeter of the second or third aspect is modified so that a cross section of an assembly composed of the phantom and the detecting section has a shape similar to a shape of a cross section of a human body.
According to the IMRT dosimeter of the fourth aspect of the present invention, at first, there may be obtained advantages similar to those of the IMRT dosimeter of the second or third aspect of the present invention. In addition, because the shape of the cross section of the assembly composed of the phantom and the detecting section is similar to that of the human body, the absorption dose distribution in the human body for the IMRT may be correctly evaluated, before the patient is actually exposed to the radiation beam in accordance with the treatment plan.
In an IMRT dosimeter of a fifth aspect of the present invention, the IMRT dosimeter of any one of the first to fourth aspects is modified so that (i) the incident direction of the radiation beam is fixed to a direction perpendicular to an upper surface of an (or the) assembly composed of the phantom and the detecting section when the integrated three-dimensional absorption dose distribution is measured, (ii) while the integrated three-dimensional absorption dose distribution in the phantom is obtained by summing (or combining, or synthesizing) the three-dimensional absorption dose distribution data in consideration of an incident angle of a radiation which has been planed for the IMRT.
According to the IMRT dosimeter of the fifth aspect of the present invention, at first, there may be obtained advantages similar to those of the IMRT dosimeter of any one of the first to fourth aspects of the present invention. In addition, the three-dimensional absorption dose distribution data can be measured without changing the incident direction of the radiation beam toward the phantom and the detecting section, when the radiation beams are applied in various incident directions. Accordingly, the integrated three-dimensional absorption dose distribution for the IMRT can be accurately measured in a short period while simplifying the construction of the radiation generator or the IMRT dosimeter.